Firebox heat pattern in a furnace



S@pt. 7, 1965 B. E. STONE 3,204,611

FIREBOX HEAT PATTERN IN A FURNACE Filed May 28, 1963 2 Sheets-Sheet 1 INVENTOR.

B. E. STON E A TTORNEKS m- 7, 1965 B. E. STONE 3,204,611

FIREBOX HEAT PATTERN IN A FURNACE Filed May 28, 1963 2 Sheets-Sheet 2 F TEAM 8 O|L j AIR GAS

FIG. 2

A 00 I600 c (I 2 I400 5 I300 11 A 2 1200 L2 A woo woo

FIRST END CENTER SECOND END OF FURNACE OF FURNACE OF FURNACE FIG. 3

INVENTOR. B. ESTONE A 7 TORNE Y5 United States Patent 3,204,611 FIREEU X HEAT PATTERN TN A FURNACE Bruce E. Stone, Kansas City, Kane, assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 28, I963, Ser. No. 283,752 3 Claims. (Cl. 122-236) The invention relates to a method and means for improving the heat pattern or temperature profile in a furnace. In one aspect the invention relates to improving the temperature profile in a combination convection-radiant furnace for heating a bank of heat exchange tubes.

Furnaces which utilize both convection and radiant heating for heating and cracking of hydrocarbons to more valuable products are used extensively in the oil industry as well as in other heating applications. Oil is conventionally heated in such furnaces for further processing such as thermal and catalytic cracking, vacuum reducing of topped crude oil and other processes.

In the vacuum reduction or vacuum flashing of topped crude oil to produce heavy gas oils for feed to a catalytic cracking process and a residuum of asphalt, it is desirable to heat the topped crude charge to a temperature just below the cracking temperature of the charge and to pass the heated charge into the vacuum distillation apparatus in as short a time as practical and at as low a pressure as practical. The topped crude oil charge is usually heated in a tube furnace wherein the heat exchange tubes define a serpentine path through the furnace. Steam is often admitted to the oil charge passing through the furnace to suppress cracking of the oil in the furnace tubes.

The present invention is applicable to a box-type tube furnace which is end fired with oil burners and is side fired with radiant-type gas burners. The oil is preheated in the top section of the furnace above the firebox and is then heated in banks of tubes horizontally positioned along the walls of the furnace surrounding the firebox section of the furnace. The furnace is rectangular in shape with the sides being substantially longer than the ends.

I have discovered that the firebox temperature profile can be improved substantially by injecting steam into the sides of the firebox adjacent the fiame issuing from the end oil burners and perpendicular to the flame emanating from the oil burners. I have found that the injection of steam into the end portions of the firebox as described not only lowers the firebox temperature at the center portion of the firebox but raises the firebox temperature at the end portions of the firebox thereby tending to level out the temperature profile across the longitudinal dimension of the firebox. I have further found that steam injection according to the invention permits an increase in the amount of oil fuel charged to the end oil burners without raising the temperature of the firebox at the center portion above the maximum desired temperature and also makes possible the processing of an increased amount of topped crude charge.

The side gas burners are of the screen type. A typical burner is a Selas Corporation Refrak screen burner as described in Bulletin ZOS-C of the Selas Corporation of America, Philadelphia, Pennsylvania.

The end oil burners are conventional oil burners. A typical burner is a John Zink Company series CBM combination gas and oil burner which is oil fired, as described in Bulletin CBM-l of John Zink Company, Tulsa, Oklahoma.

The steam nozzle at the end of the steam injection conduit can be the open end of the steam conduit or any type of restriction if the steam conduit is of such size as requires restriction. The amount of steam will usually be from 2500 to 10,000 pounds per hour (lb./hr.).

It is an object of this invention to provide a method and means for improving the temperature profile in the firebox of a furnace. It is also an object of this invention to improve the heating properties of a furnace fired by a combination of oil burners and gas burners. Still another object of the invention is to provide a furnace having improved heating properties for heating the topped crude charge to a vacuum flasher. Other objects and advantages will be apparent to one skilled in the art upon study of this disclosure including the detailed description of the invention and the appended drawing wherein:

FIGURE 1 is a perspective view, partly in section, of a furnace according to the invention;

FIGURE 2 is a horizontal cross section in plan view of the firebox of the furnace of FIGURE 11; and

FIGURE 3 is a graphic illustration of the temperature profile of the furnace.

Referring now to FIGURE 1, a furnace It) has insulated walls 11 enclosing a firebox section 12 and 'a convection heating section 13 wherein heat exchange tubes 14 are heated by combustion of fuel in side gas burners 15 and end oil burners 16. Flue gases are removed by means of stack 17. Steam is admitted into the firebox 12 via conduits 18 and nozzles 19.

The relationship of the steam nozzles to the end burners is shown in FIGURE 2. Oil is supplied to the end burners by a manifold 21 and gas is supplied to the side burners by manifold 22. The steam conduits I8 terminate in a nozzle 19. The floor 20 of the furnace is insulated with insulation similar to that employed for insulating the walls Jill. A center bridge wall 23 is positioned in the firebox section 12 between the opposite rows of gas burners 15.

The following example will be helpful in attaining an understanding of the invention but should not be considered as unduly limiting the invention.

EXAMPLE Table Run 1 Run 2 Feed to furnace, bb]./hr 480 555 Feed temperature, F 227 156 Furnace outlet temperature, 820 832 Furnace stack temperature, F 925 920 Steam to firebox, lb./hr 0 5, 000 Firebox temperature (1st; end), F. 1,240 1, 500 Firebox temperature (center), F 1, 660 1, 610 Firebox temperature (2nd end), F 1, 160 1, 475

The firebox temperature was determined by thermocouples positioned in the center and end portions of the furnace and these temperatures are shown graphically in FIGURE 3. It should be noted that steam injection benefitted the temperature profile of the furnace firebox to the extent that the topped crude charged to the furnace could be increased by 1,800 barrels per day even though the temperature of the oil charged to the furnace was considerably lower than in the run where steam is not used.

That which is claimed is:

1. The method of improving the temperature pattern in a tube furnace having a housing, a firebox in said housing, a bank of heat-exchange tubes supported adjacent the housing Walls, outlet means from said housing, an oil burner positioned in each end of said housing and projecting into said firebox, a gas burner positioned in each side of said housing about the center thereof and projecting into said firebox, comprising injecting an amount of steam sufficient to increase the temperature of the end portions of the firebox and reduce the temperature of the center portion of the firebox, into the end portions of the firebox substantially at a right angle to the flame emanating from the oil burner and into admixture with the oil emanating from the oil burner.

2. A tube furnace comprising a housing; a firebox in said housing; a bank of heat-exchange tubes supported adjacent the housing Walls; outlet means from said housing; an oil burner positioned in each end of said housing and projecting into said firebox; a gas burner positioned in each side of said housing about the center thereof and projecting into said firebox; and steam injection means positioned in each side of and adjacent the end of the housing for injecting steam into the firebox at a point into admixture with the oil emanating from the oil burner and at substantially a right angle to the flame emanating from the oil burner in an amount sufiicient to increase the temperature of the end portions of the firebox and to reduce the temperature of the center portion of the firebox.

3. A tube furnace comprising a housing; a firebox in n to it said housing; a bank of heat-exchange tubes supported adjacent the housing walls; outlet means from said housing; an oil burner positioned in each end of said housing and projecting into said firebox; a gas burner positioned in each side of said housing about the center thereof and projecting into said firebox; and steam injection means positioned in each side of and adjacent the end of the housing for injecting steam into the firebox at a point into admixture With the oil emanating from the oil burner and at substantially a right angle to the flame emanating from the oil burner in an amount sufficient to increase the temperature of the end portions of the firebox and reduce the temperature of the center portion of the firebox to permit an increase in the amount of oil fuel charged to the oil burner.

References tilited hy the Examiner UNITED STATES PATENTS 2,077,676 4/37 Darling 15874 2,102,876 12/37 Barnes 122-356 2,184,465 12/39 Ocon 122356 2,294,977 9/42 Garrison et al. 122356 PERCY L. PATRICK, Primaiy Examiner.

RENIJETE'I W. SERAGUE, ROBERT A. OLEARY,

Examiners. 

1. THE METHOD OF IMPROVING THE TEMPERATURE PATTERN IN A TUBE FURNACE HAVING A HOUSNG, A FIREBOX IN SAID HOUSING, A BANK OF HEAT-EXCHANGE TUBES SUPPORTED ADJACENT THE HOUSING WALLS, OUTLET MEANS FROM SAID HOUSING, AN OIL BURNER POSITIONED IN EACH END OF SAID HOUSING AND PROJECTING INTO SAID FIREBOX, A GAS BURNER POSITIONED IN EACH SIDE OF SAID HOUSING ABOUT THE CENTER THEREOF AND PROJECTING INTO SAID FIREBOX, COMPRISING INJECTING AN AMOUNT OF STEM SUFFICIENT TO INCREASE THE TEMPERATURE OF THE END PORTIONS OF THE FIREBOX AND REDUCE THE TEMPERATURE OF THE CENTER PORTION OF THE FIREBOX, INTO THE END PORTION OF THE FIREBOX SUBSTANTIALLY AT A RIGHT ANGLE TO THE FLAME EMANATING FROM THE OIL BURNER AND INTO ADMIXTURE WITH THE OILE EMANATING FROM THE OILE BURNER. 